Wednesday, November 13, 2013

Another Freeze Warning for Thursday Morning

By Jay Grymes & Steve Caparotta

Regardless of whether your neighborhood actually dipped to freezing or not this morning, there’s no denying that it was a very cold start to the day!  The thermometer dipped to 32° at BR’s Metro Airport and down to 31° at McComb (Pike Co.) Airport.  Fortunately, it was a very brief event and by 8AM just about everyone was back above 32°. 

The winds eased up a bit overnight and into the early morning, just enough to let most of the northern half of the viewing area experience a light freeze this morning.  Yet it didn’t get cold enough long enough to so much as ice-over the bird bath.  Based on WAFB Weather Watchers and on-line weather stations across the region, it looks like few communities on the south side of the I-10/12 corridor reached freezing this morning -- and if they did, it likely lasted for less than an hour.
Mainly sunny skies today helped to push afternoon temps climb into the mid to upper 50°s for most of us, but not everyone is finished with freezing temperatures just yet.  The National Weather Service (NWS) has posted another FREEZE WARNING for Thursday morning across portions of the viewing area.  Thursday’s FREEZE WARNING is limited to communities along and north of the I-10/12 and, unlike this morning’s WARNING, does not include Ascension and Iberville parishes this go-around.
 As Steve Caparotta noted Tuesday, during many of these multi-day freeze events, the ‘coldest’ morning is often the second morning -- after the chilling air mass has had time to settle over the area and after the winds have backed down.  With these Arctic and polar air masses, the winds often remain elevated for a number of hours after the front moves through.  Higher winds keep the lower levels of the atmosphere mixed, and that can reduce how quickly temperatures fall near the surface.
Why are winds important?  During these cold snaps -- and especially under clear skies -- the air becomes coldest right along the ground surface and actually gets warmer and warmer as you climb in elevation above the ground.  (Remember, the air temperature that we report from our stations is typically measured at roughly 4 to 5 feet above the ground.) Under light-wind to calm conditions, the air temperature at the lower levels of the atmosphere falls as the ground cools.  By comparison, under windier conditions, the warmer air from above is constantly being mixed downward, slowing the rate at which the air in the lowest levels can cool.
That brings us to our Thursday morning FREEZE WARNING. 
Tonight’s and tomorrow’s early morning winds will be lighter than what we saw for Wednesday morning, the skies will be clear once again, and Thursday will be the second day of the season’s first real chill -- that points to a good chance for colder start on Thursday morning compared to earlier this morning.
In fact, while the NWS has included fewer parishes in the FREEZE WARNING area for Thursday, they have extended the warning ‘window’ from midnight until 9AM (compared to 2AM to 9AM for Wednesday’s WARNING). 
What may limit just how cold it can get for Thursday morning is that the core of the coldest air has moved farther to the east today and will continue to do so overnight.  Based on that, we’re thinking that WAFB viewers well to the north and east of metro Baton Rouge can expect a slightly colder and longer-duration light freeze for Thursday morning.  For metro BR, it should be something similar to Wednesday’s brief freeze, while many viewers to the west of Baton Rouge may miss out on a Thursday freeze altogether. 
In the end, regardless of where you live in WAFB-land, Thursday’s chill will be nothing of serious concern -- just another very cold start to the day.
We’ll see some mainly-high clouds returning on Thursday, and we’ll bounce back into the 60°s for the afternoon highs.  Everyone will say ‘goodbye’ to the winter-like temperatures as the warming trend continues, delivering 70°s for Friday, Saturday and Sunday with morning lows in 60°s by the weekend.
We’ll also see rain chances increasing as we head towards the weekend as well, although the guidance remains mixed as to what to expect in terms of rain for Friday and the weekend.  A series of disturbances will keep the Gulf Coast weather unsettled for Friday and Saturday, with isolated showers in the forecast for both days and then “rain likely” for Sunday.
Also over the weekend, a storm system will be organizing over the Plains, with our next frontal passage expected during the day Monday.  And unlike Wednesday’s cold front, rain appears likely with Monday’s front.
So, we can consider this week as our first ride on the traditional cold-season weather roller coaster that we know so well!  And by the middle of next week, on the heels of Monday’s front, we’ll go through another big dip on the temperature coaster!

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